Various processes have been devised to produce alumina from bauxite for eventual reduction into aluminum. The process which has been most widely utilized by conversion facilities has been the Bayer process for the production of alumina. One way of maintaining product quality in the Bayer process is to utilize what are known as Kelly type pressure filters in the alumina extraction process. In particular, these filters provide a means of removing the insoluble bauxite residues ("red mud") from the desirable alumina bearing liquor in the process stream by direct pressure filtration. In particular, the bauxite ore is reacted continuously with a caustic soda stream to extract hydrated alumina in digester pressure vessels. This process step dissolves the hydrated alumina to enable the alumina to be separated from the insoluble residues and be drawn off in a process liquor for precipitation of alumina trihydrate particles. The Kelly type pressure filters incorporate leaf type filter elements in a pressure vessel which remove the red mud particles without causing an interruption in process flow which would reduce production of liquor containing dissolved hydrated alumina. After alumina trihydrate particles are precipitated from this process, rotary kilns are used to convert this precipitate to aluminum oxide, which is the final product of the conversion plants. This aluminum oxide is utilized by aluminum producers as the basic material for reduction into pure aluminum.
In a process utilizing a Kelly type pressure filter arrangement, the red mud residues form a cake on cloth covered leaf frames as the clarified liquor containing the dissolved alumina passes through the system. Since this mud cake builds up on the filter cloths, the filtration rate decreases down to a certain point at which the filter assembly must be drained and the cloth filters must be washed with dilute process liquor. After this point in the process, the filter assembly must be cleaned of red mud residue before the filtration cycle can be repeated. Most prior art practices have utilized personnel equipped with high pressure water hoses to wash the caked red mud off of the filter leaves and out of the filter shell assembly. This particular method has resulted in considerable downtime in the production process and consequent difficult working conditions for the personnel involved. Such items as physical exertion, exposure to heat and process liquor splashes and poor visibility due to the vapors generated by the cleaning have severely detracted from the performance of the process personnel. Generally, the downtime required for the cleaning operations has been approximately 20 to 30 minutes for each filter assembly. Various difficulties have been encountered with manual cleaning which result in certain parts of the filter assembly not always being hosed clean. Mud deposits which have been overlooked have quickly formed hard scale deposits and buildup which have resulted in high maintenance costs and low productivity of the equipment. Filter cloths have had to be replaced at a fairly high rate utilizing such a cleaning process in order to maintain an adequate flow throughout the process.
It is a principal object of the present invention to provide an apparatus for removing residue deposits on pressure filters which significantly reduces the time necessary for cleaning the filters.
It is an additional principal object of the present invention to provide an apparatus as aforesaid which enables such improved cleaning of deposit residue filters to be performed with greatly improved efficiency.
It is a further object of the present invention to provide an apparatus as aforesaid which can utilize semiautomatic and automatic control mechanisms to reduce or eliminate human error in the cleaning of deposit residue filters.
It is an additional object of the present invention to provide an apparatus as aforesaid which increases productive time in the filter process and thus increases capacity of the process.
Further objects and advantages of the present invention will become more apparent from a consideration of the following specification.